Why do second leads get so much love?

The pattern I keep seeing among the fans is that if male lead is a yandere/toxic they get so much hate like there is no end but if it’s the second lead that is toxic or something I see things like “oh that’s kind of hot” and get excused for their behavior.

And I also see people usually say like “oh I wish he’s the ml” “ml is kind bland” but if the specific ml was the second lead or its second lead with ml design they would get a lot of love😭

And there are also people who usually like bland second lead who are absolute green flag and if the ml is red flag they would like second lead more but if roles were switched I feel like people would like the toxic second lead more instead of the bland ml.